#coding=utf-8
from time import time
class Cache:
    '''簡單的緩存系統'''
    def __init__(self):
        '''初始化'''
        self.mem = {}
        self.time = {}

    def set(self, key, data, age=-1):
        '''保存鍵為key的值，時間位age'''
        self.mem[key] = data
        if age == -1:
            self.time[key] = -1
        else:
            self.time[key] = time() + age
        return True

    def get(self,key):
        '''獲取鍵key對應的值'''
        if key in self.mem.keys():
            if self.time[key] == -1 or self.time[key] > time():
                return self.mem[key]
            else:
                self.delete(key)
                return None
        else:
            return None

    def delete(self,key):
        '''刪除鍵為key的條目'''
        del self.mem[key]
        del self.time[key]
        return True

    def clear(self):
        '''清空所有緩存'''
        self.mem.clear()
        self.time.clear()